# Copyright 2013, Michael H. Goldwasser
#
# Developed for use with the book:
#
#    Data Structures and Algorithms in Python
#    Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser
#    John Wiley & Sons, 2013
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

from .priority_queue_base import PriorityQueueBase
from ..positional_list import PositionalList
from ..exceptions import Empty


class SortedPriorityQueue(PriorityQueueBase):  # base class defines _Item
	"""A min-oriented priority queue implemented with a sorted list."""

	# ------------------------------ public behaviors ------------------------------
	def __init__(self):
		"""Create a new empty Priority Queue."""
		self._data = PositionalList()

	def __len__(self):
		"""Return the number of items in the priority queue."""
		return len(self._data)

	def add(self, key, value):
		"""Add a key-value pair."""
		newest = self._Item(key, value)  # make new item instance
		walk = self._data.last()  # walk backward looking for smaller key
		while walk is not None and newest < walk.element():
			walk = self._data.before(walk)
		if walk is None:
			self._data.add_first(newest)  # new key is smallest
		else:
			self._data.add_after(walk, newest)  # newest goes after walk

	def min(self):
		"""Return but do not remove (k,v) tuple with minimum key.

		Raise Empty exception if empty.
		"""
		if self.is_empty():
			raise Empty('Priority queue is empty.')
		p = self._data.first()
		item = p.element()
		return (item._key, item._value)

	def remove_min(self):
		"""Remove and return (k,v) tuple with minimum key.

		Raise Empty exception if empty.
		"""
		if self.is_empty():
			raise Empty('Priority queue is empty.')
		item = self._data.delete(self._data.first())
		return (item._key, item._value)
